Fig. 4. Role of Su(Hw) and Mod(mdg4) in the regulation of ASC. (A) Schematic presentation of the yellow/ac/sc region in the previously described y, ac and sc mutants (Campuzano et al., 1985). The coordinates of the ASC region are as defined in Campuzano et al. Vertical arrows indicate the positions of chromosomal breakpoints associated with the y^3P, sc^v2 and sc⁸ mutations. The localization of the sc² and sc⁵ deletions is indicated by an elongated open box (Campuzano et al., 1985). Arrows with a triangle show insertions of P elements associated with duplication of the yellow sequences. Relative orientations of P elements are indicated by arrows in boxes. Thick horizontal white arrows show the positions and direction of yellow and ASC genes transcripts. The gray oval indicates the putative Su(Hw) binding sites in the 125 bp DNA fragment. (B) The effect of the su(Hw) (su(Hw)^v/su(Hw)^f and su(Hw)^v/su(Hw)²) and mod(mdg4) (mod(mdg4)^u1/mod(mdg4)^u1 and mod(mdg4)^u1/Df(3R)GC14) mutations on the phenotype of the mutations in ASC. The su(Hw)^v/su(Hw)^f and su(Hw)^v/su(Hw)² transheterozygous lines had similar effects on the mutations in ASC. Phenotypes of the indicated sc mutations were examined in males. The standard nomenclature for bristles whose formation is regulated by ac are as follows (Lindsley and Zimm, 1992): ADC, anterior dorsocentral; PDC, posterior dorsocentral; PSA, posterior supraalar; AVT, anterior vertical; MC, the rows of microchaetae on the notum. Other designations as in Fig. 1. Only affected bristles in ac and sc mutations are shown. Bristle pigmentation: w-v, weak variegation indicates that 1-3 bristles in thorax and head are yellow; m-v, mild variegation shows that about half of bristles are yellow; +, wild-type pigmentation of all bristles. Viability: +, about normal viability; -, lethal. The figures indicate viability for combination of mod(mdg4)^u1/mod(mdg4)^u1 with sc², i.e. ratio of sc² males to yw males obtained in the progeny of heterozygous yw/sc²; mod(mdg4)^u1/mod(mdg4)^u1 females. The total number of sc² and yw males scored is shown in brackets.